CN113557401B

CN113557401B - Hydrocarbon gas processing method and apparatus

Info

Publication number: CN113557401B
Application number: CN202080020527.4A
Authority: CN
Inventors: J·A·安吉亚诺; J·D·威尔金森; H·M·哈德森
Original assignee: UOP LLC
Current assignee: Honeywell UOP LLC
Priority date: 2019-03-11
Filing date: 2020-03-09
Publication date: 2022-08-26
Anticipated expiration: 2040-03-09
Also published as: MX2021010986A; WO2020185649A1; CN113557401A; SA521430275B1; MY195957A; US11578915B2; US20200292230A1; CA3132386A1

Abstract

A process and apparatus for recovering components from a hydrocarbon gas stream split into a first stream and a second stream is disclosed. The first stream is cooled, expanded to lower pressure, and supplied to a fractionation column. The second stream is cooled and separated into a vapor stream and a liquid stream. The vapor stream is split into two portions. The first portion is cooled, expanded to column pressure, and supplied to the column at an upper column mid-feed position. The second portion and the liquid stream are expanded to the column pressure and supplied to the column. After heating, compression, and cooling, a portion of the overhead vapor is cooled, expanded, and supplied to the column at an overhead feed position. The amount and temperature of the feed to the column maintains the overhead temperature of the column, thereby recovering a substantial portion of the desired components.

Description

Hydrocarbon gas processing method and apparatus

Background

The present invention relates to a method and apparatus for separating hydrocarbon-containing gas. Applicants claim the benefit of prior U.S. provisional application No. 62/816,711 filed on 11/3/2019 under section 119(e) of title 35 of the U.S. code.

Ethylene, ethane, propylene, propane and/or heavier hydrocarbons may be recovered from a variety of gases, such as natural gas, refinery gases and synthesis gas streams obtained from other hydrocarbon materials such as coal, crude oil, naphtha, oil shale, tar sands and lignite. Natural gas typically has a significant portion of methane and ethane, i.e., methane and ethane together comprise at least 50 mole percent of the natural gas. Natural gas also contains relatively small amounts of heavier hydrocarbons such as propane, butanes, pentanes, etc., as well as hydrogen, nitrogen, carbon dioxide, and/or other gases.

The present invention relates generally to improving the recovery of ethylene, ethane, propylene, propane and heavier hydrocarbons from such gas streams. A typical analysis of the gas stream to be treated according to the invention will be 79.1% methane, 10.0% ethane and other C in mol% ₂ Component (C), 5.4% propane and others ₃ Component, 0.7% isobutane, 1.6% n-butane and 1.1% pentane +, the balance consisting of nitrogen and carbon dioxide. Sometimes sulfur-containing gases are also present.

The present invention relates generally to the recovery of ethylene, ethane, propylene, propane and heavier hydrocarbons from such gas streams. Historical periodic fluctuations in the price of both natural gas and its Natural Gas Liquids (NGL) constituents sometimes reduce the incremental value of ethane, ethylene, propane, propylene, and heavier components as liquid products. This leads to a need for: processes that can provide more efficient recovery of these products, processes that can provide efficient recovery with lower capital investment, and processes that can be easily adapted or adjusted to vary the recovery of specific components over a wide range. Useful processes for separating these materials include gas-based cooling and freezing, oil absorption, and cooled oil absorption. In addition, cryogenic processes have become popular because economical equipment can be used that generates electricity while expanding and extracting heat from the gas being processed. Each of these processes or a combination thereof may be employed depending on the pressure of the gas source, the abundance of the gas (ethane, ethylene, and heavier hydrocarbons content), and the desired end product.

The cryogenic expansion process is now generally preferred for natural gas liquids recovery because it offers the greatest simplicity and ease of start-up, flexibility of operation, excellent efficiency, high safety and reliability. U.S. patent nos. 3,292,380, 4,061,481, 4,140,504, 4,157,904, 4,171,964, 4,185,978, 4,251,249, 4,278,457, 4,519,824, 4,617,039, 4,687,499, 4,689,063, 4,690,702, 4,854,955, 4,869,740, 4,889,545, 5,275,005, 5,555,748, 5,566,554, 5,568,737, 5,771,712, 5,799,507, 5,881,569, 5,890,378, 5,983,664, 6,182,469, 6,578,379, 6,712,880, 6,915,662, 7,191,617, 7,219,513, 8,590,340, 8,881,549, 8,919,148, 9,021,831, 9,021,832, 9,052,136, 9,052,137, 9,057,558, 9,068,774, 9,074,814, 9,080,810, 9,080,811, 9,476,639, 9,637,428, 9,783,470, 9,927,171, 9,933,207, 9,939,195, 10,227,273, 10,533,794, 10,551,118, and 10,551,119; reissue U.S. patent No. 33,408; and co-pending published patent application numbers US20080078205a1, US20110067441a1, US20110067443a1, US20150253074a1, US20160069610a1, US20160377341a1, US20180347898a1, US20180347899a1, and US20190170435a1 describe related processes (although the description of the invention is in some cases based on different processing conditions than those described in the referenced US patents and co-pending patent applications).

In a typical low temperature expansion recovery process, the feed gas stream under pressure is cooled by heat exchange with other streams of the process and/or an external refrigeration source, such as a propane compression refrigeration system. As the gas is cooled, the liquid may condense and contain the desired C ₂ The high pressure liquid of some of the + components is collected in one or more separators. Depending on the abundance of gas and the amount of liquid formed, the high pressure liquid may be expanded to a lower pressure and fractionated. The evaporation that occurs during the expansion of the liquid results in further cooling of the stream. In some conditions, it may be desirable to pre-cool the high pressure liquid prior to expansion in order to further reduce the temperature resulting from the expansion. An expanded stream comprising a mixture of liquids and vapors is fractionated in a distillation (demethanizer or deethanizer) column. Distilling the expanded cooled stream in a distillation column to separate residual methane, nitrogen and other volatile gases as overhead vapors from the vapor streamDesired C as a bottom liquid product ₂ Component C ₃ Separating the components from the heavier hydrocarbon components, or separating residual methane, C ₂ Components, nitrogen and other volatile gases as overhead vapor with the desired C as a bottom liquid product ₃ The components are separated from the heavier hydrocarbon components.

If the feed gas is not completely condensed (usually not completely condensed), the vapor remaining from the partial condensation may be split into two streams. A portion of the vapor passes through a work expander or motor or expansion valve to a lower pressure at which additional liquid is condensed as a result of further cooling of the stream. The pressure after expansion is substantially the same as the pressure at which the distillation column is operated. The combined vapor-liquid phase resulting from the expansion is supplied as a feed to the distillation column.

The remainder of the vapor is cooled to substantial condensation by heat exchange with other process streams, such as a cold fractionation column overhead. Some or all of the high pressure liquid may be combined with the vapor portion prior to cooling. The resulting cooled stream is then passed through a suitable expansion device, such as an expansion valve, to achieve the pressure at which the demethanizer is operated. During expansion, a portion of the liquid will vaporize, resulting in cooling of the total stream. The flash expanded stream is finally supplied as overhead feed to the demethanizer. Typically, the vapor portion of the flash expanded stream and the overhead vapor of the demethanizer are combined in the upper separator section of the fractionation column into a residual methane product gas. Alternatively, the cooled and expanded stream can be supplied to a separator to provide a vapor stream and a liquid stream. The vapor is combined with the overhead and the liquid is supplied to the distillation column as an overhead distillation column feed.

In the ideal operation of such a separation process, the residue gas leaving the process will contain substantially all of the methane in the feed gas with substantially no heavier hydrocarbon components, and the bottoms fraction leaving the demethanizer will contain substantially all of the heavier hydrocarbon components with substantially no methane or volatile components. However, in practice, since the conventional demethanizer operates mainly as a stripping column, it cannot be obtainedThis is the ideal case. Thus, the methane product of the process typically comprises the vapor leaving the overhead fractionation stage of the distillation column, as well as the vapor that has not been subjected to any rectification steps. C ₂ 、C ₃ And C ₄ There is a substantial loss of + components because the overhead liquid feed contains significant amounts of these components and heavier hydrocarbon components, resulting in a corresponding balance of C in the vapor leaving the overhead fractionation stage of the demethanizer ₂ Component C ₃ Component C ₄ Components and heavier hydrocarbon components. If the vapor rises, it can be associated with a large amount of C that can be absorbed from the vapor ₂ Component C ₃ Component C ₄ The loss of these desired components can be significantly reduced by liquid (reflux) contact of the components with the heavier hydrocarbon components.

In recent years, preferred processes for hydrocarbon separation use an upper absorber section to provide additional rectification of the rising vapor. For many of these processes, the source of the reflux stream for the upper rectification section is a recycle stream of residual gas supplied under pressure. The recycled residue gas stream is cooled to substantially condense, typically by heat exchange with other process streams such as cold fractionation overheads. The resulting substantially condensed stream is then passed through a suitable expansion device, such as an expansion valve, to achieve the pressure at which the demethanizer is operated. During expansion, a portion of the liquid will typically vaporize, resulting in cooling of the total stream. The flash expanded stream is ultimately supplied as an overhead feed to the demethanizer. Typical process schemes of this type are disclosed in the following documents: U.S. patent nos. 4,889,545, 5,568,737, 5,881,569, 9,052,137 and 9,080,811; and "Efficient High Recovery of Liquids from Natural Gas using High Pressure absorbers" by Mowrey, E.Ross (effective, High Recovery of Liquids from Natural Gas utilization a High Pressure Absorber), recorded in the eighty-th annual meeting by the Association of Natural Gas processors, Inc. held in Dallas, Tex, 2002, 3 months, 11 days to 13 days. Unfortunately, these processes require the use of a compressor to provide the motive force for recycling the reflux stream to the demethanizer in addition to the additional rectification section in the demethanizer, thereby increasing the capital and operating costs of the facilities using these processes.

However, according to U.S. patent nos. 4,157,904 and 4,278,457 (and other processes), many gas treatment facilities have been constructed in the united states and other countries/regions that do not have an upper absorber section to provide additional rectification of the ascending vapor and cannot be easily modified to add this feature. In addition, these facilities typically do not have excess compression capacity to allow recycle of the reflux stream, nor do their demethanizers or deethanizer columns have excess fractionation capacity to accommodate the increase in feed rate that results when a new reflux stream is added. Thus, these facilities are operating to recover C from the gas ₂ Inefficient in the recovery of components and heavier components (commonly referred to as "ethane recovery") and operates to recover only C from the gas ₃ Components and heavier components (commonly referred to as "ethane rejection") are particularly inefficient.

The present invention also employs an upper rectification section (or in some embodiments a separate rectification column) and a recycle stream of residual gas supplied under pressure. However, the majority of the reflux for this upper rectification section is provided by cooling the stream derived from the feed gas to substantial condensation and then expanding the stream to the operating pressure of the fractionation column. During expansion, a portion of the stream is vaporized, resulting in cooling of the total stream. At the upper column intermediate feed point, the cooled expanded stream is supplied to the column along with condensed liquid (which is primarily liquid methane) in the recycle stream in the overhead column feed, which can then be used to absorb C from vapors rising through the upper rectification section ₂ Component C ₃ Component C ₄ Components and heavier hydrocarbon components, thereby trapping these valuable components in the bottoms liquid product from the demethanizer.

The present invention is also a novel apparatus providing additional rectification that can be easily added to existing gas treatment facilities to increase the desired C ₂ Component (A) and (C) ₃ Recovery of components without the need for additional compression or fractionation capacity. The incremental value of this increased recovery is often significant.

According to the present invention, it has been found that more than 92% C can be obtained ₂ Recovery and C over 99% ₃ And C ₄ And (4) recovering rate. Furthermore, the invention allows methane (or C) to be produced at the same energy requirement as compared to the prior art ₂ Component) and lighter components with C ₂ Component (or C) ₃ Components) and heavier components while increasing the level of recovery. The invention is suitable for lower pressures and higher temperatures, when required at-50 DEG F to-46 DEG C]Or cooler NGL recovery column overhead temperature from 400psia to 1500psia [2,758kPa (a) to 10,342kPa (a)]Or higher ranges, are also particularly advantageous.

For a better understanding of the invention, reference is made to the following examples and accompanying drawings. Referring to the drawings:

FIG. 1 is a flow diagram of a prior art natural gas processing facility according to U.S. Pat. Nos. 4,157,904 or 4,278,457;

FIG. 2 is a flow diagram of a prior art natural gas processing facility suitable for operation according to U.S. Pat. No. 5,568,737;

FIG. 3 is a flow diagram of a natural gas processing facility according to the present invention; and is provided with

Fig. 4-6 are flow diagrams illustrating the application of the alternative apparatus of the present invention to a natural gas stream.

In the following description of the above figures, a table summarizing the calculated flow rates for representative process conditions is provided. In the tables shown herein, the values of the flow rates (in moles/hour) have been rounded to the nearest whole number for convenience. The total stream flow rates shown in the tables include all non-hydrocarbon components and are therefore generally greater than the sum of the stream flow rates for the hydrocarbon components. The temperatures shown are approximate values rounded to the nearest degree. It should also be noted that the process design calculations performed to compare the processes depicted in the figures are based on the assumption that there is no heat leakage from the ambient to the process or vice versa. The quality of commercially available insulation makes this a very reasonable assumption and is a common assumption made by those skilled in the art.

For convenience, process parameters are reported in both traditional English units and International units (SI) units. The molar flow rates given in the table may be interpreted as either pound moles per hour or kilogram moles per hour. The energy consumption reported in Horsepower (HP) and/or thousand english heating units per hour (MBTU/Hr) corresponds to the molar flow rate in pounds of moles per hour. The energy consumption reported in kilowatts (kW) corresponds to the molar flow rate in kilograms of moles per hour.

Description of the prior art

FIG. 1 is a schematic diagram showing the recovery of C from natural gas using the prior art according to U.S. Pat. Nos. 4,157,904 or 4,278,457 ₂ A process flow diagram for the design of a treatment facility for the + component. In this process simulation, the inlet gas was at 120 deg.F [49 deg.C ] as stream 31]And 790psia [5,445kPa (a)]And (4) entering the facility. If the inlet gas contains a concentration of sulfur compounds that would prevent the product stream from meeting specification, the sulfur compounds are removed by appropriately pretreating the feed gas (not shown). In addition, the feed stream is typically dehydrated to prevent hydrate (ice) formation under cryogenic conditions. Solid desiccants are commonly used for this purpose.

Feed stream 31 is cooled in heat exchanger 10 by heat exchange with a cooled residue gas (stream 39a), pumped liquid product at 48 ° F [9 ℃ (stream 42a), demethanizer reboiler liquid at 21 ° F [ -6 ℃ (stream 41), -demethanizer side reboiler liquid at 42 ° F [ -41 ℃ (stream 40), and propane refrigerant. It is to be noted that in all cases the

exchangers

10 and 12 represent a large number of single heat exchangers or single multi-channel heat exchangers, or any combination thereof. (the decision as to whether to use more than one heat exchanger for the indicated cooling service will depend on a number of factors, including but not limited to inlet gas flow rate, heat exchanger size, stream temperature, etc..) stream 31a then enters separator 11 at-28 ° F [ -33 ℃ and 765psia [5, 275kpa (a) ], where the vapor (stream 32) is separated from the condensed liquid (stream 33).

The vapor from separator 11 (stream 32) is split into two

streams

34 and 37. The liquid from separator 11 (stream 33) is optionally split into two

streams

35 and 38. (if stream 35 comprises any portion of the separator liquid, then the figure 1 process is in accordance with U.S. patent No. 4,157,904. otherwise, the figure 1 process is in accordance with U.S. patent No. 4,278,457). For the process shown in fig. 1, stream 35 does not comprise any portion of the total separator liquid. Stream 34, comprising 28% of the total separator vapor, is passed in heat exchange relationship with the cold residue gas (stream 39) through heat exchanger 12 where it is cooled to substantial condensation. The resulting substantially condensed stream 36a at-141F [ -96 ℃ ] is then flash expanded through expansion valve 13 to the operating pressure of fractionation column 17 (203psia [1,398kpa (a) ]). During expansion, a portion of the stream is vaporized, resulting in cooling of the total stream. In the process shown in fig. 1, expanded stream 36b exiting expansion valve 13 reaches a temperature of-174 ° F [ -114 ℃ ] and is supplied to separator segment 17a in the upper region of fractionation column 17. The liquid separated therein becomes the top feed of the rectifying section 17 b.

The remaining 72% of the vapor from separator 11 (stream 37) enters work expansion machine 14 where mechanical energy is extracted from this portion of the high pressure feed. Machine 14 expands the vapor substantially isentropically to column operating pressure with work expansion cooling expanded stream 37a to-115 ° F [ -82 ℃ ]. Typical commercially available expanders are capable of recovering about 80% to 85% of the work theoretically available in ideal isentropic expansion. The recovered work is typically used to drive a centrifugal compressor (such as item 15) that can be used, for example, to recompress the residue gas (stream 39 b). The partially condensed expanded stream 37a is then supplied as feed to fractionation column 17 at an upper column intermediate feed point. The remaining separator liquid in stream 38, if any, is expanded to the operating pressure of fractionation column 17 by expansion valve 16, thereby cooling stream 38a to-72F [ -58 c ], which is then supplied to fractionation column 17 at a lower mid-column feed point.

The demethanizer in column 17 is a conventional distillation column that includes a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing. The fractionation column may be comprised of three sections, as is often the case in natural gas processing facilities. The upper section 17a is a separator into which a partially vaporized overhead feed is dividedA respective vapor portion and a liquid portion, and wherein the vapor rising from intermediate rectification or absorption section 17b combines with the vapor portion of the overhead feed to form a cold demethanizer overhead vapor (stream 39) exiting the top of the column. The intermediate rectification (absorption) section 17b includes trays and/or packing to provide the necessary contact between the expanded stream 37a and the upwardly rising vapor portion of the expanded stream 38a, and to allow cold liquid to fall downward to condense and absorb C ₂ Component C ₃ Components and heavier components. The lower demethanization or stripping section 17c includes trays and/or packing and provides the necessary contact between the downwardly falling liquid and the upwardly rising vapor. The demethanizer section 17c also includes a reboiler (such as the aforementioned reboiler and side reboiler and optional supplemental reboiler 18) that heats and vaporizes a portion of the liquid flowing down the column to provide stripping vapor flowing up the column to strip methane and lighter components of the liquid product, stream 42.

The liquid product stream 42 exits the bottom of the column at 37F [3℃ ], based on typical specifications for a methane concentration of 0.5% by volume in the bottom product. The residue gas (demethanizer overhead vapor stream 39) passes countercurrently with the incoming feed gas in heat exchanger 12 and heat exchanger 10, with the residue gas being heated from-156 ° F-104 ℃ to-57 ° F-49 ℃ in heat exchanger 12 (stream 39a) and the residue gas being heated to 110 ° F [43 ℃ in heat exchanger 10 (stream 39 b). The residue gas is then recompressed in two stages. The first stage is a compressor 15 driven by an expander 14. The second stage is a compressor 19 driven by a supplemental power source that compresses the residue gas (stream 39d) to sales pipeline pressure. After cooling to 125 ° F [52 ℃) in the discharge cooler 20, the residual gas product (stream 39e) flows at 1065psia [7,341kpa (a) ] to the sales gas pipeline sufficient to meet pipeline requirements (typically at about inlet pressure).

A summary of the flow rates and energy consumption of the process shown in fig. 1 is shown in the following table:

TABLE I

(FIG. 1)

Summary of flow rates-pound moles/hour [ kilogram moles/hour ]

Recovery rate

Ethane 85.65%

99.68 percent of propane

Butane + 99.99%

Power of

By (based on unscrupulated flow rate)

FIG. 2 is a process flow diagram illustrating the improvement of the performance of the process of FIG. 1 to recover more C in the bottoms liquid product ₂ An apparatus for dispensing a composition. Fig. 1 may be adapted to use the process of U.S. patent No. 5,568,737 as shown in fig. 2. The feed gas compositions and conditions considered in the process shown in fig. 2 are the same as those in fig. 1. Thus, the process of fig. 2 can be compared to the process of fig. 1. In the simulation of this process, as in the simulation of the process of fig. 1, the operating conditions were selected to maximize the recovery level for a given energy consumption.

Most of the process conditions shown in the process of fig. 2 are almost the same as the corresponding process conditions of the process of fig. 1. The main difference is the addition of a rectification column 25 that uses the recycle stream from the residue gas as its overhead feed to recover additional C from the fractionation column 17 overhead vapor stream 39 ₂ Components and heavier components, the fractionation column overhead vapor stream is supplied to the rectification column 25 as its bottoms feed.

The rectification overhead vapor stream 152 exits the upper region of rectification column 25 at-156F [ -105 ℃ C ] and is directed into heat exchanger 23, where it provides cooling to partially cooled recycle stream 151a and partially cooled stream 36a, and then heated stream 152a at-70F [ -57 ℃ C ] is split into stream 156 and stream 157. Stream 156 flows to heat exchanger 22 where it is heated to 120 ° F [49 ℃ c ] as it provides cooling to recycle stream 151, while stream 157 flows to heat exchanger 12 and heat exchanger 10 as previously described. The resulting

warm streams

156a and 157b recombine to form stream 152b at 105 ° F [40 ℃) which will be compressed and cooled as previously described to form stream 152 e. Stream 152e is then split to form recycle stream 151 and residual gas product (stream 153).

Recycle stream 151 is cooled to-151F [ -102 c ] and substantially condensed in heat exchanger 22 and heat exchanger 23, and then flash expanded by expansion valve 24 to the operating pressure of rectifier 25 (227psia [1,563kpa (a)) (slightly below the operating pressure of fractionator 17). During expansion, a portion of the stream is vaporized, resulting in cooling of the total stream. In the process shown in fig. 2, the expanded stream 151c exiting expansion valve 24 is cooled to-175F [ -115 c ] and supplied as an overhead feed to rectification column 25.

The rectification column 25 is a conventional absorption column that includes a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing. As is often the case in natural gas processing facilities, a rectification column may be composed of two sections. The upper section is a separator wherein the partially vaporized overhead feed is separated into its respective vapor and liquid portions, and wherein the vapor rising from the lower rectification section combines with the vapor portion of the overhead feed to form a rectification overhead vapor (stream 152) exiting the top of the column. The lower rectification section includes trays and/or packing and provides the necessary contact between the liquid falling downward and the vapor rising upward so that the cold liquid reflux from stream 151C absorbs and condenses C rising in the rectification section of rectification column 25 ₂ Component C ₃ Components and heavier components. Leaving the bottom of the rectification column 25 at-149 deg.F-100 deg.C]Is pumped to a higher pressure by pump 26 (stream 154)And combined with the flash expanded stream 36c at-168 deg.F-111 deg.C]The resulting stream 155 is supplied to the fractionation column 17 at the top feed point of the fractionation column.

A summary of the flow rates and energy consumption of the process shown in fig. 2 is shown in the following table:

TABLE II

(FIG. 2)

Summary of flow rates-pound moles/hour [ kilogram moles/hour ]

Recovery rate

Ethane 86.77%

100.00 percent of propane

Butane + 100.00%

Power of

By (based on unscrupulated flow rate)

A comparison of tables I and II shows that the process of figure 2 increases the recovery of ethane from 85.65% to 86.77%, the recovery of propane from 99.68% to 100.00%, and the recovery of butane + from 99.99% to 100.00% compared to the process of figure 1. A comparison of tables I and II also shows that these increased product yields are achieved without the use of additional power.

Detailed Description

Figure 3 shows a flow diagram of a process according to the invention. The feed gas compositions and conditions considered in the process shown in fig. 3 are the same as those in fig. 1 and 2. Thus, the advantages of the present invention can be illustrated by comparing the FIG. 3 process with the FIG. 1 and FIG. 2 processes.

Most of the process conditions shown in the process of fig. 3 are almost the same as the corresponding process conditions of the process of fig. 2. The main differences are the arrangement of the flash expanded substantially condensed stream 34c, and the new overhead feed to the fractionation column 17 formed from a portion of the feed gas (stream 162) and the pumped liquid from the rectification column 25 (stream 154 a). In the fig. 3 process, feed gas stream 31 is split into two streams, stream 161 and stream 162. Stream 161 is directed to heat exchanger 10 to be cooled, as previously described, and enters separator 11 at-24 ° F [ -31 ℃ c ] and 759psia [5, 232kpa (a) ], for separation into vapor stream 32 and liquid stream 33. The subsequent treatments received for

streams

32 and 33 are almost identical to the previous ones.

However, the partially cooled stream 34a at-44F < - > 42 ℃ is further cooled to-159F < - > 106 ℃ and substantially condensed in heat exchanger 23, and then flash expanded by expansion valve 27 to the operating pressure of rectifier 25 (222psia 1,531kPa (a)) (slightly below the operating pressure of fractionator 17). During expansion, a portion of the stream may be vaporized, resulting in cooling of the total stream. In the process shown in fig. 3, the expanded stream 34c exiting expansion valve 27 is cooled to-172F [ -113 c ] and directed to a column intermediate feed point on rectification column 25.

Another portion of the feed gas (stream 162) is directed to heat exchanger 22 and heat exchanger 23 and cooled to-159 ° F [ -106 ℃) and substantially condensed (stream 163 a). Stream 163a is then flash expanded through expansion valve 13 to slightly above the operating pressure of fractionation column 17 (227psia [1,565kpa (a) ]). During expansion, a portion of stream 163b may be vaporized, resulting in cooling of the total stream to-168 ° F [ -111 ℃). Recycle stream 151 is likewise cooled to-159F [ -106 c ] and substantially condensed in heat exchanger 22 and heat exchanger 23, and then flash expanded through expansion valve 24 to the operating pressure of rectifier 25. During expansion, a portion of the stream may be vaporized, resulting in cooling of the total stream. In the process shown in FIG. 3, the expanded stream 151c at-177F [ -116℃ ] exiting expansion valve 24 is directed to the top feed point on rectifier 25.

At-130 DEG F-90 DEG C]Is withdrawn from an upper region of the fractionation column 17 and is directed to a bottom feed point of the rectification column 25. The rectification column 25 is a conventional absorption column that includes a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing. As is often the case in natural gas processing facilities, a rectification column may be composed of two sections. The upper section is a separator wherein the partially vaporized overhead feed is separated into its respective vapor and liquid portions, and wherein the vapor rising from the lower rectification section combines with the vapor portion of the overhead feed to form a rectification overhead vapor (stream 152) exiting the top of the column. The lower rectification section includes trays and/or packing and provides the necessary contact between the downwardly falling liquid and the upwardly rising vapor so that the cold liquid reflux from streams 151C and 34C absorbs and condenses C rising in the rectification section of rectification column 25 ₂ Component C ₃ Components and heavier components. The bottom of the column 25 is at-132 deg.F < -91 deg.C]Is pumped to a higher pressure by pump 26 and combined with flash expanded stream 163b, at-151F-102 c]The resulting stream 155 is supplied to the fractionation column 17 at the top feed point of the fractionation column.

The rectification overhead vapor stream 152 exits the upper region of the rectification column 25 at-164F < -109 > C and is directed into heat exchanger 23 wherein it provides cooling to the partially cooled recycle stream 151a, the partially cooled portion of the feed gas (stream 163), and the partially cooled stream 34a, and then the heated stream 152a at-44F < -42 > C is split into stream 156 and stream 157. Stream 156 flows to heat exchanger 22 where it is heated to 109 ° F [43 ℃) as it provides cooling to recycle stream 151 and a portion of the feed gas (stream 162), while stream 157 flows to heat exchanger 12 and heat exchanger 10, as previously described. The resulting

warm streams

156a and 157b recombine to form stream 152b at 108 ° F [42 ℃ c ], which as previously described will be compressed and cooled to form stream 152e at 125 ° F [52 ℃ c ] and 1065psia [7,341kpa (a) ]. Stream 152e is then split to form recycle stream 151 and residual gas product (stream 153).

A summary of the flow rates and energy consumption of the process shown in fig. 3 is shown in the following table:

TABLE III

(FIG. 3)

Summary of flow rates-pound moles/hour [ kilogram moles/hour ]

Recovery rate

Ethane 92.40%

100.00 percent of propane

Butane + 100.00%

Power of

By (based on unscrupulated flow rate)

The performance boost of the present invention is unexpectedly large in magnitude relative to the performance boost of the prior art. A comparison of tables I and III shows that the process of figure 3 increases the ethane recovery from 85.65% to 92.40% (an increase of approximately 7 percentage points), the propane recovery from 99.68% to 100.00%, and the butane + recovery from 99.99% to 100.00% compared to the process of figure 1. Comparison of tables I and III also shows that these increased product yields are achieved without the use of additional power. The present invention represents a very significant 8% improvement in terms of recovery efficiency (defined by the amount of ethane recovered per unit power) compared to the prior art of the process of figure 1.

A comparison of tables II and III shows that the process of figure 3 increases the recovery of ethane from 86.77% to 92.40% (an increase of over 5 percentage points) and the recovery of propane and butane + is unchanged (100.00%) compared to the process of figure 2. Comparison of tables II and III also shows that these increased product yields are achieved without the use of additional power. In terms of recovery efficiency (defined by the amount of ethane recovered per unit power), the present invention represents a very significant 6% improvement over the prior art of the fig. 2 process.

The improvement in recovery efficiency of the present invention over the prior art process can be understood by examining the improvement in rectification provided by the present invention as compared to the rectification section 17b of the process of fig. 1 and 2 and the rectification column 25 of the process of fig. 2. While the fig. 1 process has a single reflux stream (stream 36b) for its rectification section 17b in column 17, the present invention has three reflux streams (stream 151c and stream 34c of rectification column 25, and stream 155 of rectification section 17b in column 17). Not only is the total reflux of the present invention greater (61% higher), its overhead reflux stream (stream 151C) is of much better quality because it is almost pure methane, while the overhead reflux stream 36b of the fig. 1 process contains 10% higher C ₂ Components and heavier components.

Although the fig. 2 process is an improvement over the fig. 1 process with its dual reflux stream (stream 151c of rectification column 25 and stream 155 of rectification section 17b in column 17), the total amount of reflux is 23% less than the triple reflux stream of the present invention. In addition, the single reflux stream supplied to rectifier 25 for the fig. 2 process is only 25% of the total reflux supplied to rectifier 25 of the present invention, making it less capable of rectifying the overhead vapor stream 39 from column 17. The rectification column 25 of the present invention also has less stream 39 to be rectified first because it uses a portion of the feed gas (the substantially condensed expanded stream 163b) to provide partial rectification of the column vapor in the rectification section 17b of the column 17, such that less rectification is required in the column 25. The combination of these factors leads to C of the present invention ₂ The increase in component recovery was almost 7 percentage points over the process of figure 1 and 5 percentage points over the process of figure 2.

An important advantage of the present invention is how it can be easily incorporated into existing gas treatment facilities to achieve the superior performance described above. As shown in fig. 3, only six connections (commonly referred to as "accesses") to existing facilities are required in the following respects: split for feed gas (stream 162), for partially condensed stream (stream 34a), for pumped liquid from rectification column 25 (stream 154a), overhead vapor for fractionation column 17 (stream 39), for heated residual gas (stream 156a), and for compressed recycle gas (stream 151). When new heat exchanger 22 and heat exchanger 23, column 25 and pump 26 are installed near the fractionation tower 17, the existing facilities can continue to operate, with only a short period of facility shutdown when installation is complete to make a new connection to these six existing pipes. The plant can then be restarted with all existing equipment remaining in service and operating exactly as before, except that product recovery is now higher without an increase in compression power.

Another advantage of the present invention is that because a portion of the feed gas (stream 162) is split around existing heat exchangers and separators, there is less flow through existing facilities, which results in a lower vapor/liquid stream volume within fractionation column 17. This means that if there is reserve compression power available for higher feed gas throughput, it is possible to process more feed gas and increase processing facility revenue without eliminating existing plant bottlenecks.

Other embodiments

The present invention is also applicable to a new facility as shown in fig. 4 and 6. Depending on the amount of heavier hydrocarbons in the feed gas and the feed gas pressure, the cooled feed stream 161a (fig. 4) or feed stream 31a (fig. 6) exiting heat exchanger 10 may not contain any liquid (because it is above its dew point, or because it is above its critical condensation pressure). In such a case, the separator 11 shown in fig. 4 and 6 is not required.

The splitting of the feed gas according to the invention can be achieved in several ways. In the processes of fig. 3 and 4, the splitting of the feed gas occurs prior to any cooling of the feed gas. In such cases, cooling and substantial condensation of a portion of the feed gas in multiple heat exchangers, such as heat exchanger 22 and heat exchanger 23 shown in fig. 3 or heat exchanger 22 and heat exchanger 12 shown in fig. 4, may be advantageous in some situations. However, the feed gas may also be split after cooling (but before separating any liquid that may have formed), as shown in fig. 5 and 6.

The high pressure liquid (stream 33 in fig. 3 and 4) need not be expanded and fed to the distillation column at the mid-column feed point. Instead, all or a portion thereof can be combined with the portion of the cooled feed gas (stream 162a) exiting heat exchanger 22 in fig. 3 and 4. (this is illustrated by dashed stream 35 in fig. 3 and 4.) any remaining portion of the liquid (stream 38 in fig. 3 and 4) may be expanded by a suitable expansion device, such as expansion valve 16 or an expansion machine, and fed to an intermediate column feed point (stream 38a) on the distillation column. Stream 38 can also be used for inlet gas chilling or other heat exchange services before or after the expansion step and then passed to the demethanizer.

As previously described, a portion of the feed gas (stream 162) and a portion of the separator vapor (stream 34) are substantially condensed, and the resulting condensate is used to absorb the valuable C's from the vapor ₂ Component C ₃ Components and heavier components that rise through rectification section 17b of demethanizer 17 (fig. 4 and 6) or through rectification column 25 and rectification section 17b of column 17 (fig. 3 and 5). However, the present invention is not limited to this embodiment. It may be advantageous to treat only a portion of these vapors or to use only a portion of the condensate as absorbent in this manner, for example, in cases where other design considerations indicate that these vapors or portions of the condensate should bypass the rectification section 17b of demethanizer 17 (fig. 4 and 6) or in cases where the rectification column 25 and/or the rectification section 17b of column 17 (fig. 3 and 5).

Feed gas conditions, facility size, available equipment, or other factors may dictate that it is feasible to eliminate working expander 14 or replace it with an alternative expansion device, such as an expansion valve. Although separate stream expansion is shown in a particular expansion device, alternative expansion devices may be employed where appropriate. For example, conditions may ensure working expansion of a substantially condensed portion of the separator vapor (stream 34b in fig. 3 and 5 and stream 34a in fig. 4 and 6) or a substantially condensed portion of the feed stream (stream 163a in fig. 3 and 4 and stream 162a in fig. 5 and 6).

According to the present invention, external refrigeration may be used to supplement the cooling available to the inlet gas, separator vapor, and/or recycle streams from other process streams, particularly in the case of enriched inlet gas. The use and distribution of the separator liquid and demethanizer side draw liquids for process heat exchange, as well as the particular arrangement of heat exchangers for inlet gas and separator vapor cooling, and the selection of process streams for particular heat exchange services, must be evaluated for each particular application.

It will also be appreciated that the relative amount of feed present in each branch of the split vapor feed will depend on several factors, including gas pressure, feed gas composition, heat that can be economically extracted from the feed, and the amount of horsepower available. More feed to the top of the column may increase recovery while reducing power recovered from the expander, thereby increasing recompression horsepower requirements. Increasing the feed to the lower portion of the column reduces horsepower consumption, but may also reduce product recovery. The relative position of the mid-column feed may vary depending on the inlet composition or other factors such as the desired level of recovery and the amount of liquid formed during cooling of the inlet gas. Furthermore, two or more feed streams or portions thereof may be combined depending on the relative temperatures and amounts of the individual streams, and the combined stream then fed to the column intermediate feed position.

The invention provides C based on the utility consumption required to operate the process ₂ Component C ₃ Component (C) and heavier hydrocarbon component or ₃ Improved recovery of components and heavier hydrocarbon components. The improvement in utility consumption required to operate the process may be in the form of reduced compression or recompression power requirements, reduced external refrigeration power requirements, reduced supplemental heating energy requirements, or a combination thereof.

While there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto, for example, to adapt the invention to various conditions, feed types, or other requirements, without departing from the spirit of the invention as defined by the following claims.

Claims

1. Will contain methane, C ₂ Component C ₃ Process for the separation of a gas stream of components and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C ₂ Component C ₃ Component (C) and heavier hydrocarbon component or said C ₃ A component and a heavier hydrocarbon component, wherein

(a) Cooling the gas stream under pressure to provide a cooled stream;

(b) said cooled stream is expanded to lower pressure whereby it is further cooled; and

(c) said further cooled stream is directed to a distillation column and fractionated at said lower pressure whereby said components in said relatively less volatile fraction are recovered;

the improvement wherein, prior to cooling, the gas stream is split into a first stream and a second stream;

(1) said first stream is cooled to form a substantially condensed first stream;

(2) said substantially condensed first stream is expanded to said lower pressure to form an expanded substantially condensed first stream, whereupon said expanded substantially condensed first stream is supplied to said distillation column at an intermediate column feed position;

(3) said second stream is cooled under pressure sufficiently to form a partially condensed second stream;

(4) said partially condensed second stream is separated, thereby providing a vapor stream and at least one liquid stream;

(5) said vapor stream is divided into a first portion and a second portion;

(6) said first portion is cooled to form a substantially condensed first portion;

(7) said substantially condensed first portion is expanded to said lower pressure to form an expanded substantially condensed first portion, whereupon said expanded substantially condensed first portion is supplied to said distillation column at an upper mid-column feed position above said mid-column feed position;

(8) said second portion is expanded to said lower pressure to form an expanded second portion, which is supplied to said distillation column at a lower mid-column feed position below said mid-column feed position;

(9) at least a portion of said at least one liquid stream is expanded to said lower pressure to form an expanded liquid stream that is supplied to said distillation column at another lower mid-column feed position below said mid-column feed position;

(10) collecting a distillation vapor stream from an upper region of said distillation column and heating to form a heated distillation vapor stream, said heating thereby providing at least a portion of said cooling of steps (1), (3), and (6);

(11) said heated distillation vapor stream is compressed to higher pressure, cooled, and then divided into said volatile residue gas fraction and a compressed recycle stream;

(12) said compressed recycle stream is cooled to form a substantially condensed compressed recycle stream, said cooling thereby providing at least a portion of said heating of step (10);

(13) said substantially condensed compressed recycle stream is expanded to said lower pressure to form an expanded substantially condensed compressed recycle stream, whereupon said expanded substantially condensed compressed recycle stream is supplied to said distillation column at a top column feed position; and is

(14) The quantities and temperatures of the feed streams to the distillation column are effective to maintain the overhead temperature of the distillation column at a temperature whereby a substantial portion of the components in the relatively less volatile fraction are recovered.

2. The method of claim 1, wherein

(1) Said gas stream is cooled under pressure sufficiently to form a partially condensed gas stream;

(2) said partially condensed gas stream is divided into said first stream and said second stream; and

(3) said second stream is separated, thereby providing said vapor stream and said at least one liquid stream.

3. The method of claim 1, wherein

(1) Said first stream is combined with at least a portion of said at least one liquid stream to form a combined stream;

(2) cooling the combined stream to form a substantially condensed combined stream;

(3) said substantially condensed combined stream is expanded to said lower pressure to form an expanded substantially condensed combined stream, whereupon said expanded substantially condensed combined stream is supplied to said distillation column at said mid-column feed position; and

(4) any remaining portion of said at least one liquid stream is expanded to said lower pressure to form said expanded liquid stream.

4. The method of claim 1, wherein

(1) Said expanded substantially condensed first portion is supplied at a mid-column feed position to a contacting and separating device that produces said distillation vapor stream and a bottom liquid stream, whereupon said bottom liquid stream is supplied to said distillation column at said top column feed position;

(2) an overhead vapor stream is withdrawn from said upper region of said distillation column and is supplied to said contacting and separating device at a lower column feed position below said mid-column feed position;

(3) said expanded substantially condensed compressed recycle stream is supplied to said contacting and separating device at a top column feed position; and is

(4) The quantities and temperatures of the feed streams to the contacting and separating device are effective to maintain the overhead temperature of the contacting and separating device at a temperature whereby a substantial portion of the components in the relatively less volatile fraction are recovered.

5. The method of claim 4, wherein

6. The method of claim 4, wherein

(3) said substantially condensed combined stream is expanded to said lower pressure to form an expanded substantially condensed combined stream, whereupon said expanded substantially condensed combined stream is supplied to said distillation column at said top column feed position; and

7. Will contain methane, C ₂ Component C ₃ Apparatus for the separation of a gas stream of components and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C ₂ Component C ₃ Component (C) and heavier hydrocarbon component or said C ₃ Components and heavier hydrocarbon components, in which apparatus are presentLower device

(a) First cooling means for cooling said gas stream under pressure, said first cooling means being connected to provide a cooled stream under pressure;

(b) first expansion means connected to said first expansion means to receive at least a portion of said cooled stream under pressure and expand it to lower pressure, whereby said stream is further cooled; and

(c) a distillation column connected to said distillation column to receive said further cooled stream, said distillation column adapted to separate said further cooled stream into said volatile residue gas fraction and said relatively less volatile fraction;

the improvement wherein said apparatus comprises

(1) First dividing means located before said first cooling means for dividing said gas stream into a first stream and a second stream;

(2) heat exchange means connected to said first dividing means to receive said first stream and cool it sufficiently to form a substantially condensed first stream;

(3) said first expansion means being connected to said heat exchange means, said first expansion means being adapted to receive said substantially condensed first stream and expand it to said lower pressure to form an expanded substantially condensed first stream, said first expansion means being further connected to said distillation column to supply said expanded substantially condensed first stream to said distillation column at a mid-column feed position;

(4) said first cooling means being connected to said first dividing means to receive said second stream and cool it under pressure sufficiently to form a partially condensed second stream;

(5) separating means connected to said first cooling means to receive said partially condensed second stream and separate it into a vapor stream and at least one liquid stream;

(6) second dividing means connected to said separating means to receive said vapor stream and divide it into a first portion and a second portion;

(7) said heat exchange means being further connected to said second dividing means to receive said first portion and cool it sufficiently to form a substantially condensed first portion;

(8) second expansion means connected to said heat exchange means to receive said substantially condensed first portion and expand it to said lower pressure to form an expanded substantially condensed first portion, said second expansion means being further connected to said distillation column to supply said expanded substantially condensed first portion to said distillation column at an upper mid-column feed position above said mid-column feed position;

(9) third expansion means connected to said second dividing means to receive said second portion and expand it to said lower pressure to form an expanded second portion, said third expansion means being further connected to said distillation column to supply said expanded second portion to said distillation column at a lower mid-column feed position below said mid-column feed position;

(10) fourth expansion means connected to said separating means to receive at least a portion of said at least one liquid stream and expand it to said lower pressure to form an expanded liquid stream, said fourth expansion means being further connected to said distillation column to supply said expanded liquid stream to said distillation column at another lower mid-column feed position below said mid-column feed position;

(11) vapor withdrawing means connected to said distillation column to receive a distillation vapor stream from an upper region of said distillation column;

(12) said heat exchange means being further connected to said vapor withdrawing means to receive said distillation vapor stream and heat it to form a heated distillation vapor stream, thereby to supply at least a portion of said cooling of (2) and (7);

(13) compressing means connected to said heat exchange means to receive said heated distillation vapor stream and compress it to higher pressure to form a compressed heated distillation vapor stream;

(14) second cooling means connected to said compressing means to receive said compressed heated distillation vapor stream and cool it to form a cooled compressed heated distillation vapor stream;

(15) third dividing means connected to said second cooling means to receive said cooled compressed heated distillation vapor stream and divide it into said volatile residue gas fraction and a compressed recycle stream;

(16) said heat exchange means being further connected to said third dividing means to receive said compressed recycle stream and cool it sufficiently to form a substantially condensed compressed recycle stream, thereby to supply at least a portion of said heating of (12);

(17) fifth expansion means connected to said heat exchange means to receive said substantially condensed compressed recycle stream and expand it to said lower pressure to form an expanded substantially condensed compressed recycle stream, said fifth expansion means being further connected to said distillation column to supply said expanded substantially condensed compressed recycle stream to said distillation column at a top column feed position; and

(18) control means adapted to adjust the amount and temperature of the feed stream to the distillation column to maintain the overhead temperature of the distillation column at a temperature whereby the major portion of the components in the relatively less volatile fraction are recovered.

8. The apparatus of claim 7, wherein

(1) Said first cooling means being connected to receive said gas stream and cool it under pressure sufficiently to form a partially condensed gas stream;

(2) said first dividing means being connected to said first cooling means to receive said partially condensed gas stream and divide it into said first stream and said second stream; and is

(3) Said separating means is connected to said first dividing means to receive said second stream and separate it into said vapor stream and said at least one liquid stream.

9. The apparatus of claim 7, wherein

(1) Combining means connected to said first dividing means and said separating means to receive said first stream and at least a portion of said at least one liquid stream and form a combined stream;

(2) said heat exchange means being connected to said combining means to receive said combined stream and cool it sufficiently to form a substantially condensed combined stream;

(3) said first expansion means being connected to said heat exchange means to receive said substantially condensed combined stream and expand it to said lower pressure to form an expanded substantially condensed combined stream, said first expansion means being further connected to said distillation column to supply said expanded substantially condensed combined stream to said distillation column at said mid-column feed position; and is provided with

(4) Said fourth expansion means being connected to said separating means to receive any remaining portion of said at least one liquid stream and expand it to said lower pressure to form said expanded liquid stream.

10. The apparatus of claim 7, wherein

(1) Said second expansion means being connected to contacting and separating means to supply said expanded substantially condensed first portion to said contacting and separating means at a mid-column feed position, said contacting and separating means being adapted to produce said distillation vapor stream and a bottom liquid stream;

(2) said distillation column being connected to receive said bottom liquid stream at said top column feed position, said distillation column being adapted to separate said bottom liquid stream into an overhead vapor stream and said relatively less volatile fraction;

(3) said contacting and separating device being further connected to said distillation column to receive said overhead vapor stream at a lower column feed position below said mid-column feed position;

(4) said contacting and separating device being further connected to said fifth expansion device to receive said expanded substantially condensed compressed recycle stream and supply it to said contacting and separating device at a top column feed position; and is

(5) Said control means is adapted to adjust the amount and temperature of the feed stream to said contacting and separating means to maintain the overhead temperature of said contacting and separating means at a temperature whereby the major portion of the components in said relatively less volatile fraction are recovered.